The present invention concerns indicator lights for motor vehicles. More precisely, the invention concerns a light comprising a light source with an elongate shape overall and means for directing the radiation from the light towards the outside of the vehicle in accordance with a photometry in accordance with the regulations.
A constraint inherent in the design of indicator lights is compliance with the legally required photometry. The photometry is determined by the measurement of the light intensity intercepted by a screen placed opposite the light at a given distance facing it, and disposed transversely to the longitudinal axis of the vehicle.
The regulatory provisions thus impose minimum levels of intensity to be complied with:
at a point situated at the centre of the photometric grid (on the axis of the light),
and at points distributed around this centre. It is in particular necessary to comply with the minimum levels of intensity in a horizontal band extending on each side of the centre of the grid, so that an observer observing the light at different lateral angles whilst remaining substantially in the same horizontal plane can perceive the radiation issuing from the light. In order to comply with this second requirement it is therefore necessary to horizontally spread the beam generated by the light.
Thus, in order to comply with the legal constraints (and in order to produce light delivering an effective indicating beam), the illumination of the indicator lights must both be directed substantially in a direction parallel to the longitudinal axis thereof and have a sufficient horizontal spread (displayed by isocandela distributions on the photometry grid), and a certain, more moderate, vertical spread.
Moreover, designers are currently seeking to use sources with an elongate shape, of large size, such as low-pressure discharge lamps. These sources would be advantageous because of their low power consumption, and because of the possibilities which they offer in terms of style.
However, one problem posed by the use of such elongate light sources is satisfying the legal photometric minima, given that, at a given flux, the luminance of a source is smaller, the more extensive its surface.
In association with a rectilinear light source having great elongation, the use of a reflector in the shape of a cylinder with a parabolic base (or cylindro-parabolic reflector), whose focal line coincides with the axis of the source, could make it possible to maximise the intensity of the emission of a substantially parallel beam in order to resolve the aforementioned problem. The radiation emitted by such an optical assembly would be characterised by a high spread along the axis of the elongate source.
In the case of a source whose axis is horizontal and included in a transverse direction of the vehicle, it is thus possible to envisage obtaining a photometry in compliance with the regulations by using a cylindro-parabolic reflector.
However, in the case of an elongate light source whose axis is oriented differently, in a substantially vertical fashion, for example, additional means should also be provided for spreading the beam of the light (which is already spread significantly along the axis of the source, that is to say vertically), in the horizontal direction. These additional spreading means could be vertical cylindrical patterns (or flutes) provided on the reflector, a lens or a glass closing off the light.
A photometric grid would then be obtained which is highly dispersed because of this double spread, and a significant proportion of the flux generated by the light would be directed in directions which correspond neither to angles of observation nor to measurement points on the photometric grid in accordance with the regulations. Because of this, this significant proportion of the flux would be xe2x80x9clostxe2x80x9d and it would be necessary to oversize the light source (increasing the total intensity delivered by the source) in order to comply with the minimum intensity constraints at the centre of the grid. Such an oversizing would result in additional costs which would increase the cost price of the light, in an increase in the electrical power consumed, and in obvious problems of bulk.
One aim of the invention is to make it possible to produce a light comprising an elongate-shaped light source oriented in any manner with respect to the horizontal, producing a photometry beam in accordance with the regulations without requiring any oversizing of the source compared with a light whose similar source is oriented horizontally.
According to the present invention there is provided a motor vehicle indicator light comprising a light source of generally elongate shape, highly inclined with respect to a required beam spread direction, and a reflector in which the source is mounted, wherein the reflector comprises at least one mirror able to create, from a part of the source situated opposite it, a primary virtual light source substantially parallel to the required spread direction and means for concentrating the light radiation coming from the said primary virtual source in the vicinity of a plane containing the required beam spread direction.
Preferred but non-limitative aspects of the device according to the invention are as follows:
a series of optical cells each situated opposite a part of the light source, each cell comprising at least one mirror for creating a primary virtual light source substantially parallel to the required direction of spread and means for concentrating the light radiation coming from the said primary virtual source in the vicinity of a plane containing the required beam spread direction,
the means for concentrating the light radiation coming from the primary virtual source of an optical cell lie overlapping, in a required direction of emission (X) of the light, at least one mirror intended to create a primary virtual light source of the cell which is adjacent to it,
it comprises a reflective cover associated with the light source,
the reflector lies essentially on one side of the light source,
the light source is a low-pressure discharge tube, whose axis is separate from the vertical in a longitudinal vertical plane and/or in a transverse vertical plane,
the mirror or mirrors are disposed perpendicularly to the bisecting line of the axis of the part of the light source situated opposite the mirror or mirrors, and of an axis parallel to the required direction of spread,
the concentration means comprise a part of a reflective surface in the form of a parabolic cylinder whose focal line coincides substantially with the axis of the primary virtual source,
the concentration means comprise, in continuity with the part of a reflective surface in the form of a parabolic cylinder, a reflective surface having substantially the geometry of a semi-paraboloid, the two reflective surfaces being in continuity with each other, the focal point of the semi-paraboloid corresponding substantially to one end of the primary virtual source,
the concentration means comprise an essentially flat reflective surface for creating, from the primary virtual source, a secondary virtual source which is parallel to it, and means for rectifying the radiation reflected by the said essentially flat reflective surface,
the reflective surfaces of the reflector consist of separation surfaces between a solid material in which the source is embedded and the environment external to the light, the refractive index of the material filling the light being greater than the refractive index of the environment external to the light and the face of the light through which the light radiation emerges from the light being defined by a separation surface,
the means of rectifying the radiation are integrated into the separation surface,
the mirrors for forming a primary virtual source are plane,
the surfaces of the mirrors comprises means of spreading the light perpendicularly to the required principal beam spread direction (Y),
the said spreading means are serrations which extend generally parallel to the required principal beam spread direction (Y),
the mirrors for forming a primary virtual source are portions of a circular cylinder whose directrix extends parallel to the required principal beam spread direction (Y).